1. Field of the Invention
The invention relates to a gas-turbine construction having an air compressor, a heat exchanger connected downstream of the air compressor, a combustion chamber, and a turbine which can be driven by hot combustion gases and from which the combustion gases are fed to the heat exchanger for heating the compressed supply air coming from the air compressor.
2. Discussion of Background
Gas turbines, which are classified as heat engines, are operated with the combustion gases of liquid fuels. A typical gas-turbine construction, which is shown in FIG. 1a, has an air compressor V, also called turbocompressor, which draws in fresh air L, which is typically compressed to a pressure of 4 to 6 bar and is forced into a heat exchanger W, in which it is preheated by still hot combustion gases VG flowing from the turbine T. Finally, the preheated and compressed supply air passes together with fuels BS into the combustion chamber, in the course of which hot or combustion gases of at least 600.degree. C. are produced. These combustion gases flow with great velocity into the turbine T and drive the latter, which is normally connected to a generator G for the generation of electricity.
The efficiency of a gas turbine is all the greater, the higher is the temperature of the combustion gases entering the turbine blades and the lower is the temperature of the exhaust gases escaping into the open from the gas turbine. Therefore the still hot combustion gases issuing from the turbine blades are nearly always directed through the heat exchanger, where they can give off their waste heat largely to the fresh air delivered by the compressor before said fresh air enters the combustion chamber.
A further advantage of the heat exchangers which are also known as recuperators consists in the fact that their thermodynamic optimum can be achieved at relatively low pressure ratios, as a result of which the turbine construction only needs a few turbine stages, so that the overall construction of a gas-turbine arrangement can be of relatively simple design.
However, the operation of heat exchangers at full load is problematic, since very hot combustion gases are formed by the very high temperatures arising in the combustion chamber, and these combustion gases lead to very intense air preheating inside the heat exchanger, as a result of which, however, reliable operation with low-pollutant premix combustion processes becomes difficult.
It has been found that an important component for the optimization of gas-turbine arrangements is the heat exchanger or recuperator, which makes a substantial contribution to the efficiency of such a machine.
In contrast to the conventional type of construction of a so-called tubular heat exchanger, which, however, only has a low power density, modern, compact heat exchangers usually consist of a stack of suitably shaped plates, which are arranged in layers one above the other and in this way form through-flow ducts through which the precompressed supply air and, in the opposite direction to the direction of flow of the supply air, the hot combustion gases flow alternately.
Since the specific output of a heat exchanger of plate-shaped design primarily depends on the characteristic length of the heat-exchanger element, plate-type heat exchangers having very fine ducts with high transfer capacity are being produced nowadays.